I've written a vi plugin that adds autocompletion functionality for baan scripts. It does require a little bit of preparation though.

The script and installation instructions are available from vim.org. (http://www.vim.org/scripts/script.php?script_id=3754) or more detailed on github (https://github.com/mfussenegger/baancomplete)
Don't get scared by the early 0.2 version. It is very usable already.

The API file generation was build with LN in mind and is untested for BaanIV or 5.

I hope some of you might find it useful. And if you have any suggestions or issues just let me know.

Regards

For LN you can use ERP LN Application Studio that has a lot of built in features for 4GL: code completion, templates, outline, open declaration, global searches, etc.